Moisture content for peppermills

I picked up some 6x6 walnut from a local sawyer the other day with the intention of turning at least some of it into peppermills. He claimed it was dry, but after cutting it down it's still reading between 20-25% MC. I'm not really surprised by this, but my question is how dry does it really need to be for this application? I know bowls can be turned wet and then turned again once they're dry, but flatwork really needs <12%MC.

Worst case scenario is that I can throw it in a toaster oven I use for drying blanks for stabilizing, but I just want to know if this is necessary or not.